The invention described herein may be manufactured and used by or for the Government of the United States of America for governmental purposes without the payment of any royalties thereon or therefor.
The present invention relates to the hydrodynamics of marine vessels, more particularly to adjuncts, appendages and auxiliary devices for affecting same.
A stern flap is an extension of the hull bottom surface which extends aft of the transom. It is a relatively small appendage (typically constructed so as to include internal metal bracing beams and external metal plate material) which is fitted to the ship""s transom. Critical stern flap geometry parameters include: (i) chord length; (ii) span across the transom; and, (iii) an angle denoted as xe2x80x9ctrailing edge downxe2x80x9d (TED), referenced to the local buttock slope (run) at the transom. The main purpose of a stern flap device is to reduce the shaft power required to propel a ship through the water, thereby reducing the engine""s fuel consumption and increasing the ship""s top speed and range. The hydrodynamically significant stern flap surface is its lower surface. In principle, a stern flap is coupled with a hull stern so that the hull bottom surface and the stern flap lower surface essentially represent a kind of surface continuum, thereby effectively altering the hydrodynamic character of the hull.
The application of stern flaps to large displacement vessels is a fairly recent innovation. The U.S. Navy has been investigating the use of stern flaps on many different hull types. The standard (traditional or conventional) stern flap is designed with parallel, linear (straight) leading and trailing edges for orientation of these linear edges perpendicular to the ship centerline. Stern flaps have now been proven by the U.S. Navy to reduce the requisite amount of propulsive power during navigation, with several concomitant advantages. Stern flaps: foster reductions in operating and life-cycle costs through fuel savings; increase both ship speed and range; decrease the amount of pollutants released by ships into the atmosphere; and, reduce propeller loading, cavitation, vibration and noise tendencies.
Incorporated herein by reference is the following United States patent which is pertinent to stern flaps: Karafiath et al. U.S. Pat. No. 6,038,995 issued Mar. 21, 2000, entitled xe2x80x9cCombined Wedge-Flap for Improved Ship Powering.xe2x80x9d The following papers, each of which is incorporated herein by reference, are also pertinent to stern flaps: Karafiath, G., D. S. Cusanelli, and C. W. Lin, xe2x80x9cStern Wedges and Stern Flaps for Improved Powering xe2x80x94U.S. Navy Experience,xe2x80x9d 1999 SNAME Annual Meeting (paper), Baltimore, Md. (September 1999); Cusanelli, D. S., xe2x80x9cStern Flapsxe2x80x94A Chronicle of Success at Sea (1989-2002),xe2x80x9d SNAME Innovations in Marine Transportation, Pacific Grove, Calif. (May 2002); Cave, W. L., and D. S. Cusanelli, xe2x80x9cEffect of Stern Flaps on Powering Performance of the FFG-7 Class,xe2x80x9d SNAME Chesapeake Sect Paper, (October 1989); Cusanelli, D. S., and W. L. Cave, xe2x80x9cEffect of Stern Flaps on Powering Performance of the FFG-7 Class,xe2x80x9d Marine Technology, Vol. 30, No. 1, pp 39-50, (January 1993); Cusanelli, D. S., and K. M. Forgach, xe2x80x9cStern Flaps for Enhanced Powering Performance,xe2x80x9d Proceedings of 24th ATTC, College Station, Tex. (November 1995); Cusanelli, D. S., xe2x80x9cStern Flap Powering Performance on the PC 1 Class Patrol Coastal, Full Scale Trials and Model Experiments,xe2x80x9d PATROL ""96 Conference Proceedings, New Orleans, La., (December 1996); Cusanelli, D. S., xe2x80x9cIntegrated Wedge-Flap, an Energy Saving Device,xe2x80x9d 21st UJNR Marine Facilities Panel Meeting, Tokyo, Japan (May 1997); Cusanelli, D. S., and G. Karafiath, xe2x80x9cIntegrated Wedge-Flap for Enhanced Powering Performance,xe2x80x9d FAST ""97, Fourth International Conference on Fast Sea Transportation, Sydney, Australia, (July 1997); Cusanelli, D. S., xe2x80x9cStern Flap Installations on Three U.S. Navy Ships,xe2x80x9d ASNE 1998 Symposiumxe2x80x9421st Century Combatant Technology, Biloxi, Miss. (January 1998); Cusanelli, D. S. and L. Hundley, xe2x80x9cStern Flap Powering Performance on a SPRUANCE Class Destroyer, Full Scale Trials and Model Experiments,xe2x80x9d Research to Reality in Ship Systems Engineering Symposium, Tysons Corner, Va. (September 1998); Cusanelli, D. S. and L. Hundley, xe2x80x9cStern Flap Powering Performance on a SPRUANCE Class Destroyer, Full Scale Trials and Model Experiments,xe2x80x9d Naval Engineers Journal, Vol. 111, No. 2 (March 1999); Cusanelli, D. S., S. D. Jessup and S. Gowing, xe2x80x9cExploring Hydrodynamic Enhancements to the USS Arleigh Burke (DDG 51),xe2x80x9d FAST ""99, Fifth International Conference on Fast Sea Transportation, Seattle, Wash. (August 1999); Cusanelli, D. S., and G. Karafiath, xe2x80x9cEnergy Savings and Environmental Benefits of Stern Flaps on Navy Ships,xe2x80x9d ASNE Symposium: Marine Environmental Stewardship for the 21st Century, Arlington, Va. (October 1999); Cusanelli, D. S., and G. Karafiath, xe2x80x9cStern Flaps on Navy Ships, Fuel Savings and Environmental Benefits,xe2x80x9d IMT""99, Innovations in Marine Technology, New Orleans, La. (December 1999); Cusanelli, D. S., xe2x80x9cStern Flaps and Bow Bulbs for Existing Vesselsxe2x80x94Reducing Shipboard Fuel Consumption and Emissions,xe2x80x9d United Nations Environmental Programme (UNEP 2001), Brussels, Belgium (February 2001); Cusanelli, D. S., and G. Karafiath, xe2x80x9cStern Flapsxe2x80x9d, Professional Boat Builder Magazine, pages 81-87, (April/May 2001); Karafiath, G, D. S. Cusanelli, S. D. Jessup and C. D. Barry, xe2x80x9cHydrodynamic Efficiency Improvements to the USCG 110 Ft. WPB Island Class Patrol Boats,xe2x80x9d 2001 SNAME Annual Meeting Paper, Orlando, Fla. (October 2001).
xe2x80x9cAmphibiousxe2x80x9d U.S. Navy assault ships, designated xe2x80x9cL_xe2x80x9d ships (e.g., LHA, LSD, LHD, etc.), are primary landing ships that resemble small aircraft carriers. These amphibious ships contain massive well decks (which are accessed through one or more large folding stern gates), and are designed for putting troops on hostile shores. The present inventor was tasked to apply existing stern flap technology to xe2x80x9camphibiousxe2x80x9d U.S. Navy ships of the xe2x80x9cL_xe2x80x9d classes such as the WASP (LHD 1) Class, the WHIDBEY ISLAND (LSD 41) Class, or the HARPER""S FERRY (LSD 49) Class, wherein the hull design includes a large stern gate along with stern gate support structure (including plural support brackets) at least partially submerged aft of the transom.
The stern gate of an LHD class amphibious assault ship is typically designed to be mechanically pivotable about an axis situated in the lower part of the stern and above the waterline, thereby xe2x80x9copeningxe2x80x9d rotatingly downward-aftward and xe2x80x9cclosingxe2x80x9d rotatingly upward-forward. A sizable structural unit is attached to the ship transom to support the stern gate in its fully opened position. This stern gate support structure generally includes main support brackets, smaller bracing supports, and a large diameter protection pipe defining its perimeter. When fully closed, the stern gate is positioned in an approximately vertical position; when fully open, the stern gate is positioned in an approximately horizontal or slightly downward from horizontal position so that the lower surface of the stern gate suitably rests upon the upper surfaces of the support brackets.
Prior to the present invention, U.S. Navy investigators believed that the presence of the stern gate support structure precluded the design of shallower angled stern flaps. However, the Navy investigators perceived as a benefit a xe2x80x9cmaskingxe2x80x9d effect associated with installation of a stern flap beneath the stern gate support structure. xe2x80x9cMaskingxe2x80x9d of the stern gate support structure involved the effect of deflecting fluid flow away from the potentially high resistance components of the stern gate support structure. It was previously thought by U.S. Navy investigators that this kind of flap-underneath configuration would maximize the reduction of possible ship resistance (drag), due to the masking of the submerged stern gate support structure. Nevertheless, it eventually became apparent to U.S. Navy investigators that this masking effect (i.e., the effect of masking the drag of the stern gate support structure) did not compensate for the poor performance due to the excessive flap angle produced by installation beneath the gate supports.
The U.S. Navy conducted tests wherein several standard stern flap designs were affixed to the lower surfaces of the existing stern gate support brackets. The flaps were thereby limited to high TED angles. Although the best of these standard flap designs reduced high speed powering, the excessive TED angle produced harsh penalties at low speeds. Without exception, the installation of a standard stern flap beneath the stern gate support structure forced the flap angle (TED) to be unrealistically high, and low-speed performance was correspondingly poor. For instance, the U.S. Navy tested several standard stern flap designs on the WASP (LHD 1) class, wherein these flaps were affixed to the lower surface of the stern gate supports, thus limiting the flap to rather high TED angles of twenty degrees (20xc2x0) and above. The best among these initial standard flap designs reduced power by 6% at 24 knots, but the excessive TED angle produced unfavorable low speed penalties. On the TARAWA (LHA 1) class, a flap of standard design was reduced to a five degree TED angle, and produced much improved low speed performance, with a 2% powering reduction at 24 knots. However, stern flap design criteria for the TARAWA Class were less stringent than for the WASP Class because of certain hydrodynamic and architectural differences. In particular, the TARAWA included sectional split-gate doors not requiring submerged support structure. In contrast, the WASP folding gate, designed to service an enlarged well-deck, included submerged support structure. It is reasonable to expect that shallower TED angles than 20xc2x0 on marine vessels such as the WASP will result in greater powering reductions due to improved low speed performance than those exhibited at TED angles of 20xc2x0 and deeper.
The inventor was thus motivated by his recognition that the standard stern flap would be limitedly advantageous for the task of applying existing stern flap technology to amphibious U.S. Navy ships such as the WASP (LHD 1) Class, the WHIDBEY ISLAND (LSD 41) Class, or the HARPER""S FERRY (LSD 49) Class. A configuration involving a standard stern flap and a gated transom, wherein the standard stern flap is disposed below the transom""s gating construction in order to avoid or circumvent it, limits the theoretical potentiality of hydrodynamic benefits which could be associated with stern flap implementation. If the premise of stern flap design in amphibious ship applications is that the stern flap be designed around the existing stern gate support structure (which is partially submerged aft of the transom), then stern flap design flexibility is significantly limited. According to this circumventive design premise, installation of a standard stern flap on a gated transom having at least partially submerged bracketing structure(s) associated therewith will necessitate placement of the upper stern flap surface beneath the lower surface(s) of the stern gate""s bracketing member(s). This circumventive design approach will inevitably result in a relatively large TED angle of the stern flapxe2x80x94a design that will usually be less advantageous than if the stern flap were positioned at a relatively small TED angle. Furthermore, there are structural issues associated with such circumventive design approach. It may be problematical to complete the structural assembly so as to ensure the continued integrity of the stern gate support structure. Another limiting consideration is that the stern flap must be continually placed beneath the lower surface of the stern gate while the stern gate is in its open position; if the stern flap projects too far aft, for instance, it will impede the complete opening of the stern gate.
In view of the foregoing, it is an object of the present invention to provide an improved stern flap methodology for application to a marine vessel having an essentially flat stern which is xe2x80x9cgatedxe2x80x9d so as to have associated therewith submerged or partially submerged support structure (such as that which includes bracketing members) projecting aft of the stern, wherein such support structure is designed to be supportive of the openly positioned stern gate.
Prior to the present invention, the prevailing wisdom in the U.S. Navy was that the presence of an amphibious ship""s stern gate support structure precluded the design of shallower angled stern flaps. Previous applications of traditional stern flaps to amphibious hulls prescribed installation beneath the stern gate support structure. The present invention more fully avails itself of the potential benefits of stern flap technology. In particular, the present invention advantageously provides for the design of stern flaps characterized by the shallower angles which are necessary for the desired performance enhancement at the low to moderate ship speeds frequently navigated by these amphibious ships.
According to typical embodiments, the present invention provides an integratedly hydrodynamic and supportive structure for a gated ship stern. Application of the present invention will usually be with respect to xe2x80x9camphibious shipsxe2x80x9d and other vessels having stern gates and associated stern gate support structure including plural structural components. The present invention is applicable to any hull design which includes stern gate means (e.g., including a large stern gate such as exemplified by a WASP class ship) and stern gate support means (e.g., a stern gate support structural unit including plural bracketing members) at least partially submerged aft of the transom. This genre of hull design is exemplified by some U.S. Navy amphibious ships such as those mentioned herein.
The present invention represents a unique methodology involving the adaptation of stern flap structure to an amphibious vehicle""s gated transom characterized by supportive structure upon which a gate rests when in a fully open position. The inventor, a naval architect employed by the U.S. Navy, conceived his invention based on his realization that the application of stern flap technology to the gated transom of the Navy ships of interest (such as the WASP Class, WHIDBEY ISLAND Class or HARPER""S FERRY Class) would necessitate a new stern flap design and arrangement. The inventor initially investigated his amphibious ship stern flap concept by conducting model-scale tests on such a hullform characterized by a gated transom. The inventor thus demonstrated that the performance of a traditional flap design, when applied to this kind of hullform, was inferior to that of his new stern flap configuration.
According to many embodiments of the present invention, dual-purpose adjunctive apparatus is for being appended to the stern of a marine hull having a stern gate. The inventive apparatus comprises plural spaced bracket members and at least one stern flap member each interposedly joining two bracket members. Each bracket member has a bracket member top surface. Each stern flap member has a stern flap member bottom surface. The inventive apparatus is capable of being appended to the stern whereby the stern gate rests upon the at least two bracket member top surfaces and whereby the at least one stern flap member bottom surface interacts with the water navigated by the marine vessel, the inventive apparatus thereby being structurally supportive with respect to the stern gate and hydrodynamically influential with respect to the marine vessel.
Typical embodiments of the present invention provide an auxilliary assembly for attachment at the stern of a ship. The stern includes a stern gate pivotable about a horizontal axis between closed and open positions of the stern gate. The inventive assembly is adaptable to attachment at least substantially below the axis so as to be generally disposed projectingly aft of the stern. The assembly comprises at least three united components consisting of at least two support components and at least one hydrodynamic component. During the attachment of the inventive assembly: (a) the at least two support components and the at least one hydrodynamic component are in alternating arrangement across the stern; (b) the at least two support components generally describe a unitary support surface for supporting the stern gate when the stern gate is in an open position; and, (c) the at least one hydrodynamic component generally describes a unitary hydrodynamic surface for hydrodynamically affecting the ship when the ship is navigating.
According to some embodiments, the present invention is a method of improving the hydrodynamic quality of a vessel. The vessel includes a stern provided with a stern gate. The stern has a stern gate support device annexed thereto. The stern gate support device includes a plurality of separate approximately parallel support members, each support member protruding approximately longitudinally relative to the vessel. The method comprises integrating at least one stern flap section with the support members. The integrating includes connecting every pair of adjacent support members via a different stern flap section, the integrating thereby forming an integral unit annexed to the stern. The integral unit is characterized by supportive functionality associated with the support members and by hydrodynamic functionality associated with the at least one stern flap section. Typical of inventive method embodiments, each support member is attached to the stern. The stern gate support device further includes at least one reinforcement member, each reinforcement member being attached to at least two support members and being unattached to the stern. The inventive method further comprises removing the at least one reinforcement member prior to performing the integrating.
The present invention affords several advantages when used in association with marine vessels having a stern characterized by a gating construction. According to the present invention, the overall stern flap structure (including its lower surface, which is the hydrodynamic surface) is integrated through the stern gate support brackets, rather than installed under the brackets as in previous design attempts. The present invention allows for the hydrodynamic surface (the lower flap surface) to be installed at the shallower angles necessary for the desired performance enhancement.
Furthermore, the full-scale design of the present invention""s stern flap will permit removal of certain structural components of the original stern gate support structure. The inventive stern flap will include internal structure and top-side closing plates, which will facilitate integration within the existing stern gate support structure. Since according to this invention stern flap structure is to be situated between the stern gate support brackets, this allows for elimination of structural components such as the large diameter protection pipe and the smaller bracing supports. The elimination of these components further reduces hull resistance (drag).
Moreover, according to some embodiments the present invention""s amphibious ship stern flap can be designed with reduced span, so that the entirety of the inventive stern flap""s structure remains within the area already proscribed by the main stern gate support brackets. This design will obviate all components of the stern flap outboard of the main stern gate support brackets, thus further easing ship integration.
The inventor alludes to his invention in the paper Dominic S. Cusanelli and Gabor Karafiath, xe2x80x9cAdvances in Stern Flap Design and Application,xe2x80x9d FAST 2001 (The Sixth International Conference on Fast Sea Transportation), Southhampton, United Kingdom, Sep. 4-6, 2001, incorporated herein by reference.
The present invention bears some relation to the invention disclosed by Dominic S. Cusanelli in his U.S. nonprovisional patent application filed on Aug. 14, 2002 entitled xe2x80x9cContour Stern Flap,xe2x80x9d incorporated herein by reference.